If you follow the argument of paying more for extra or heavier bags to it's logical conclusion, it makes sense to me to charge fat people more for their seats. I don't know, perhaps use BMI numbers as a guide?

You get better health coverage rates if you are healthy right? And that includes weight. So, why not charge more for fat people on planes? Come on Rummy, in the interests of fairness my ticket is funding part of the fuel burn of someone who weighs more than they should. That's not fair.

Hmmmm.... me thinks Colonel Burch could strike it rich by setting up a line out-houses just as you enter the terminal. Poop In & Save Out.